The percentage of positive drug tests among U.S. workers has increased for the first time since 2003, according to an analysis of workplace drug testing results released by Quest Diagnostics in September. Quest, a provider of diagnostic information services, analyzed 8.5 million workplace drug test results obtained from urine, oral fluid, and hair during 2013.

The increase in positivity rates was driven by a rise in marijuana and amphetamine use. Colorado and Washington State, which legalized recreational use of marijuana in 2012, saw their positivity rates increase by double-digits in 2013. But increases in these states can’t be explained simply as an effect of legalization, since both states experienced large increases in positivity in previous years, according to Quest.

The positivity rates for amphetamines, which include methamphetamine and prescription medications, are at the highest levels ever recorded. Methamphetamine positivity rates are at their highest levels since 2007.

The data below reflect changes in positivity rates between 2013 and 2012, as identified by the Quest Diagnostics Drug Testing Index (DTI). Three major testing populations are included in DTI reports: federally mandated “safety-sensitive” workers, such as truck drivers, train operators, and nuclear power plant workers; the general work force; and the combined U.S. work force.